Page:Popular Science Monthly Volume 28.djvu/545

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Y attention was first called to this subject in 1853. At that time I was an assistant in the "Yale Analytical Laboratory," which afterward developed into the present Sheffield School. The interest of the Professor of Chemistry, John Porter, was excited by some articles on this subject which had recently appeared in France, and he was desirous of making experiments to test an idea that had occurred to himself. The sensitive surface was to be prepared while actually under the influence of colored light, so that from the start the colored rays should be able to act on it and influence the molecular condition of the newly formed combinations. A prismatic spectrum was to be employed, and it was hoped that the red rays would persuade the newly born silver salts to reflect red light and only red light, while the same salt, when generated under the influence of the green rays, by the aid of this early education was to be made capable hereafter of reflecting green light, but incapable of reflecting red, yellow, or blue light. Expressed in the language of the undulatory theory of light, the idea would be about as follows: expose molecules in act of formation to the long waves of red light, and ever after they will be capable of reflecting mainly the long waves of red light; all other kinds they will absorb and convert into heat.

This task having been assigned to me, I entered on it with zeal, and arranged a dark room; the solar spectrum was made to fall nicely on the table, and many of the processes known at that time were in succession tested. The photographs of the spectrum thus obtained were not at all uniform in color; sometimes they would be delicately shaded from a dull-red gray to a blue or violet-gray and often they presented minor changes of color variously disposed. Favorable indications were followed up as they presented themselves; but after a lime I became convinced that the play of color in the photographs was solely due to the greater or less energetic action of the light upon the sensitive substance, and that exactly the same results could be obtained by using white light, more or loss intense. When the work was finished, I presented my written report with the photographs, and the professor, after studying it, came to the same conclusion. The "nascent" idea was not feasible.

And yet photographs in color of colored objects have been obtained. Upon one occasion, about twenty-five years ago, I obtained a very fine one. The subject was a large elm-tree and a rod farm-house, these two objects filling up almost the whole plate. The ordinary wet-collodion process was employed; the negative, after being